spin_lock_string (of /include/asm-i386/spinlock.h) macro definition (not clear) of version <= 2.6.8

Sushil Mayengbam <hacker.mayengbam@xxxxxxxxx> · Tue, 5 Jan 2010 20:39:48 +0530

---------- Forwarded message ----------
From: Sushil Mayengbam <hacker.mayengbam@xxxxxxxxx>

Date: Sun, Jan 3, 2010 at 2:25 PM
Subject: spin_lock_string (of /include/asm-i386/spinlock.h) macro definition (not clear) of version <= 2.6.8
To: kernelnewbies@xxxxxxxxxxxx

Hi,
I couldn't understand the logic behind the insertion of a new subsection ".section .text.lock"   as shown below (highlighted) in the older version (<= 2.6.8). Can you please explain how this section is only called upon when the 'SIGN' bit is SET by line:58? If the 'SIGN' bit is not SET, where would the control go from line: 58?

  55#define spin_lock_string \
  56        "\n1:\t" \
  57        "lock ; decb %0\n\t" \
  58        "js 2f\n" \
  59        ".section .text.lock,\"ax\"\n" \
  60        "2:\t" \
  61        "cmpb $0,%0\n\t" \
  62        "rep;nop\n\t" \
  63        "jle 2b\n\t" \
  64        "jmp 1b\n" \
  65        ".previous"

Thanks and regards,
Sushil